FOUR-STROKE ENGINES
ELECTRIFICATION RAISES PM SHAFT GENERATOR ROLE Shaft generators are increasingly becoming part of ship electrification designs, and the advantages of permanent magnet systems are being recognised Demand for shaft generators is increasing across a wide range of vessel types, and, concerned about delivery time, Daewoo Shipbuilding & Marine Engineering (DSME) signed an MOU with Hyosung Heavy Industries in May to jointly develop domestic manufacturing capability for largecapacity permanent magnet (PM) shaft generator motors. The companies already have an arrangement for induction motors and have been supplying them to LNG, LPG and crude oil carriers. However, with the container ship market opening up, they will no longer have to rely on imported equipment for their larger power solutions. The switch to PM technology can increase fuel efficiency by about 3%, says DSME, and is more compact. PM generators are highly efficient over a wide range of speeds, says Emil Cerdier, Product Director at Berg Propulsion. Also, running smaller and/or fewer engines onboard reduces maintenance effort. “Variable speed gensets will have an increasing impact on fuel economy as the portion of power produced on a vessel shifts from main engines to gensets,” he says. Berg Propulsion is involved with an increasing number of vessels designed with more sophisticated power generation systems including hybrids combining diesel main engines with electric motors and batteries as well as fully electric-motor-powered propellers. “Direct coupled diesel engines are great for constant high load, but for situations where less power is required an electric system is often more efficient,” he says. Designing vessels with this in mind can achieve fuel savings of 20% or more. “We are continuously increasing our focus on electrical integration to offer our customers complete and optimized propulsion systems. We have active systems that adapt propulsion parameters to always seek optimum efficiency. We also have in-house comparison software to evaluate alternative propulsion and power generation concepts to help our customers find the best alternative for their specific vessel and operation profile.” Lighter, simpler and more efficient He cites a recent example of a bulk carrier currently being commissioned where the controllable pitch propellers are powered by PM motors mounted in two fins below the hull. The unique feature of the patent-pending design developed in partnership with The Switch is that the motor has no bearings of its own but rather relies on the ones in the shaft line. “We are including the power management system in our scope of supply, and with mode selection integrated in our control system it is easy for the captain to always operate the vessel in the most optimum way.” Dr Jussi Puranen Head of Product Line, Electric Machines at Yaskawa Environmental Energy/The Switch, has seen a huge shift towards PM machines in marine applications over the last five years. The main reason for this has been the power conversion efficiency of the technology. Also, PM machines are mechanically simpler and thus less likely to fail. The technology allows a reduction in generator
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size and weight by up to 50% compared to a conventional electric machine. PM machines can be applied as gensets, shaft generators or as propulsion motors to improve the energy efficiency of a vessel. Coupling a PM shaft generator with a frequency converter provides maximum freedom in optimizing engine and propeller efficiencies. These options can be particularly relevant for reefers or when a scrubber is being installed. Instead of adding gensets to cover the increased power demand, a greener and more feasible solution can be to upgrade a vessel that has a 2-stroke main engine with an in-line PM shaft generator. Puranen says that in a typical 2MW shaft generator application, a PM generator means around 50 tons less fuel burnt annually compared to conventional electrically-excited generator. “The neodymium magnets which are currently being used in high power density megawatt-class PM machines were invented in the early 80s. Since then, there have
8 A permanent magnet shaft generator from The Switch
8 Dr Jussi Puranen Head of Product Line, Electric Machines at Yaskawa Environmental Energy/The Switch
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